1. Technical Field
The present invention relates to a light emitting device, especially to an organic light emitting device having a light source which is a mixture of the light of two individual organic light en thing diode panels.
2. Description of Related Art
A light emitting diode is a solid-lighting device that has been rapidly developed in recent years; and an organic light emitting diode (OLED) is an important branch of the light emitting diode. Early organic light emitting diode such as those disclosed on U.S. Pat. No. 3,172,862 and U.S. Pat. No. 4,356,429, have disadvantages on excesses thickness (>1 μm) and high operation voltage (>100 Volt), so that it is not suitable for commercial applications. An improvement structure of the organic light emitting diode has been demonstrated by Eastman Kodak Company in 1987. The improvement structure provided by Eastman Kodak Company is to place a small molecular organic light emitting material between two electrodes. And then, a polymer light emitting diode is disclosed by Cambridge University in 1900. Since then, aggressive researches have been employed on the developments of the organic light emitting devices Therefore, a great progress have been reached on the grasp of the material characteristic and the manufacturing technology of the organic light emitting diode, and thereby making the commercial applications of the organic light diode be possible.
Singlet excited states transition and triplet excited states transition are two important fundamental light emitting mechanisms of an organic light emitting diode. A transition from a singlet excited state to a ground state is known as fluorescence; and a transition from a triplet excited state to a ground state is known as phosphorescence. Different wavelength of an emitting light can be produced by the two transition mechanisms with selection of different light emitting materials. However, the light colors seen by human eye are not a single wavelength, but a mixture of multiple wavelengths, thus the adjustment of the light color by mixing different wavelengths is an important issue. U.S. Pat. No. 5,851,063 disclosed a method for producing white light by mixing the primary colors of the light (RGB system), which uses inorganic light emitting diode as light source. Compared to the inorganic light emitting diode, organic light emitting diode has advantages on self-lighting, high brightness, high contrast, short response time, compact size, flexibility, and simple structure. The sheet type of the emitting light of an organic light emitting diode makes it suitable for lighting and flat panel display.
U.S. patent 2008/0284317A1 disclosed a light adjusting method of an organic light emitting diode, in which a fluorescent blue emission layer, a phosphorescent red emission layer, and a phosphorescent green emission layer are combined into a single organic light emitting diode. However, it is difficult to drive each emission layer with only one current/voltage source due to the different material characteristics of each emission layer. An improved organic light emitting diode structure is disclosed in U.S. Pat. No. 7,935,963. Fluorescence layers and phosphorescence layers are divided into two individual regions by an electrode layer in one organic light emitting diode. Therefore, different current/voltage sources can be applied to the fluorescence layers and the phosphorescence layers independently, and the controllability can be enhanced. The improvement structure can solve the difficulty of applying a single power source on the different emission layers, however, the emission layers are still combined in a single organic light emitting diode structure, thus the light path will be blocked, thereby reducing the light emitting efficiency.